1. Field of the Invention
The present invention is related to magnetoresistive (MR) and spin valve sensors for sensing magnetic fields, and in particular to a magnetic recording system utilizing an MR read sensor for use in high temperature environments.
2. Background Art
A magnetoresistive (MR) sensor detects magnetic fields by detecting a change in resistance of a read element. MR read sensors are used in magnetic disk and tape systems to read signals in the form of changes in magnetic flux recorded on a recording medium. Typical MR read sensors are rectangular multi-layered structures in which thin film layers are deposited on a substrate.
Presently known thin film magnetic heads, known as merged heads, include an inductive write element for recording signals and a magnetoresistive (MR) sensor for reading the recorded signals. Write operations are carried out inductively using a pair of magnetic write poles which form a magnetic path and define a transducing nonmagnetic gap in the pole tip region. The transducing gap is positioned close to the surface of an adjacent recording medium such as a rotating magnetic disk. An electrical coil formed between the poles causes flux flow in the magnetic path of the poles in response to a current in the coil that is representative of signal information to be recorded.
Read operations are carried out by the MR sensor which changes resistance in response to changes in magnetic flux on the adjacent magnetic medium. A sensing electric current passed through the MR sensor senses the resistance of the MR sensor, which changes in proportion to changes in the magnetic flux.
A greater magnetoresistance has been found in devices called giant magnetoresistive (GMR) sensors. In spin valve structures two ferromagnetic (FM) layers are separated by a copper layer. One of the two ferromagnetic layers has its magnetic moment fixed or pinned by exchange coupling to an antiferromagnetic (AFM) film. The application of an external magnetic field causes a change in the relative magnetic orientation of one of the FM layers relative to the other FM layer. This causes a change in the spin-dependent scattering of conduction electrons and therefore the electrical resistance of the device.
Magnetic storage devices such as disk drives are being used more and more in environments wherein the ambient temperature is high, perhaps 100 degrees Centigrade. If the temperature exceeds the Neel temperature of the pinning layer, the magnetic properties will be adversely affected and the disk drive will be rendered subject to errors or inoperable.
In the past, the material chosen for the antiferromagnetic (AEM) layer of a spin valve device is the alloy iron manganese (FeMn). In U.S. Pat. No. 5,552,949 to Hashimoto et al., entitled xe2x80x9cMagnetoresistance Effect Element With Improved Antiferromagnetic Layerxe2x80x9d, issued Sep. 3, 1996, the alloy iridium manganese (IrMn) was chosen to reduce the corrosive effects of the acids used in the manufacturing process. In the Hashimoto et al. patent, an MR element comprising an exchange coupled film is formed on a substrate. The exchange coupled film comprises an AFM layer made of IrMn and an FM layer at least part of which is laminated with the AFM layer. Electrodes provide an electric current to the FM layer. The AFM layer comprises Ir 100-z Mnz wherein the composition of iridium is in the range 24 less than =z less than =75. However, this composition of iridium manganese does not have a high blocking (Neel) temperature and loses desirable magnetic properties at high temperatures.
What is needed is a spin valve sensor that is fabricated of an AFM material that will not lose its magnetic properties at high operating temperatures.
In accordance with this invention, a magnetoresistive sensor device is formed with a nonmagnetic buffer layer of metal, such as tantalum (Ta), that is deposited on a substrate. A Permalloy (NiFe) film is directly deposited on a Ta layer for texturing purposes and IrMn is then deposited on the NiFe film. The AFM layer comprises Irx Mn100-x, wherein x is 15 less than x greater than 23. Electrodes are coupled to the FeMn layer.
In accordance with an embodiment of the invention the nonmagnetic buffer layer is approximately 50 Angstroms thick, and the IrMn AFM layer is approximately 100 Angstroms thick.
The invention using the Ta buffer is insensitive to temperatures as high as 295 degrees Centigrade. Without the use of the Ta buffer, the device would adversely change its magnetic performance if the temperature is raised above 200 degrees Centigrade.